Investigación

 

Raman and structural studies on the high-temperature regime of the KH₂PO₄-NH₄H₂PO₄ system

 

J.F. Juradoª*, C. Vargas-Hernándezª, and R.A. Vargas^b

 

^aLaboratorio de Propiedades Ópticas de Materiales (POM), Departamento de Física y Química, Universidad Nacional de Colombia, A.A 127, Manizales, Colombia.

^bDepartamento de Física, Universidad del Valle, A.A. 25360, Cali, Colombia.

 

Recibido el 18 de abril de 2012;
Aceptado el 24 de julio de 2012

 

Abstract

We have studied the high-temperature phase transition (HTPT) of crystalline potassium and ammonium dehydrogen phosphates and solid solutions of them with composition (1-x) KH₂ PO₄ + x NH₄ H₂ PO₄ (KADPx, for x =0.0, 0.1, 0.2, 0.3, 0.4, 0.6 and 1.0), by means of X-ray diffraction analysis at room temperature and in situ Raman spectroscopy as function of temperature. Analysis of the Raman spectra made it possible to monitor the temperature dependence of vibrational bands associated to structural changes taking place during a proposed partial dehydration reaction that starts to take place at a characteristic temperature T_p and tends to increase above it. This assignment is supported using characteristic vibrational bands of phosphates and polyphosphates (produced as a consequence of the partial dehydration reaction of the crystals above T_p). The presence of the polyphosphate vibrational bands assigned to the stretch vibration of its PO₂ species (at about 1120 cm^_1for pure KDP) accompanied by a broad band assigned to P-O-P backbone vibrations (at about 713 cm^_1for pure KDP) [14] become evident at temperature higher than T_p depending on the composition of KADPx.

Keywords: X-ray diffraction; ionic crystals; vibrational states in crystals.

 

PACS: 61.05.cp; 64.70.kp; 63.20.-e

 

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Acknowledgements

The authors wish to acknowledge the support of DIMA (Direccion de investigación, Universidad Nacional de Colombia, Sede Manizales) to research project.

 

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Note

* Author to whom correspondence should be addressed: jfjurado@unal.edu.co